1. Field of the Invention
The present invention relates to a display device, and more particularly, to a horizontal drive circuit including means for preventing a surge voltage from occurring in a switching operation, and a method therefor.
2. Description of the Related Art
A monitor (or "display"), which is a peripheral device for a computer, exhibits as a picture a varying visual display of a signal received from a computer, so that a user can recognize the visual display. FIG. 1 is a block diagram of a display. Referring to FIG. 1, the monitor includes a microcomputer 20 for receiving a horizontal synchronizing signal H-Sync and a vertical synchronizing signal V-Sync from a video card 10 contained within a computer (not shown). The microcomputer 20 generates a control signal for controlling a monitor picture. The monitor also includes vertical and horizontal deflection circuits 30 and 40 for receiving the vertical and horizontal synchronizing signals V-Sync and H-Sync, respectively. The vertical and horizontal deflection circuits 30 and 40 perform vertical and horizontal deflections, respectively, so that an electron beam generated by an electron gun of a cathode ray tube 80 is sequentially deflected from the upper left portion of the cathode ray tube 80 to its lower right portion by a defection yoke (DY in FIG. 1), to thereby form the picture.
The display also includes a high voltage circuit 50 for supplying a high voltage to an anode of the cathode ray tube 80. The high voltage circuit 50 uses a retrace line pulse generated by the output of the horizontal deflection circuit 40. A video pre-amplifier 60 is also included in the monitor, for amplifying a low level of a video signal (R,G,B) transmitted from the video card 10 using a low-voltage amplifier, to thereby maintain a predetermined voltage level. The display further includes a video main amplifier 70 for amplifying the voltage amplified by the video pre-amplifier 60 to a signal of 40 to 60 Vpp, and for supplying energy to each pixel of the display.
This display device forms an image using the electron beam projected to its fluorescent screen. Here, a circuit for deflecting the electron beam is called a deflection circuit. Generally, the deflection mode is divided into electrostatic deflection, using an electric field, and electromagnetic deflection, using a magnetic field. Electromagnetic deflection is used, for example, in a TV in which a sawtooth current flows through horizontal and vertical coils to form pictures.
A general configuration of the horizontal deflection circuit (or "horizontal deflector") 40 is shown in FIG. 2. Referring to FIG. 2, the horizontal deflection circuit 40 includes a horizontal oscillation circuit 41 which generally uses a blocking oscillation circuits A horizontal drive circuit 42 of the horizontal deflection circuit 40 provides one-stage or two-stage current amplification using a transistor TR or a field effect transistor FET. The horizontal drive circuit 42 provides a gate current sufficient for turning on/off an output transistor of a horizontal output circuit 43 and performs waveform correction.
The horizontal output circuit 43 of the horizontal deflection circuit 40 generates a sawtooth current which flows through a deflection coil using a switching operation of a transistor. The horizontal deflection circuit 40 also includes a horizontal size controller 44, connected to the horizontal output circuit 43, to maintain a specific horizontal size of the picture of the display device.
The image resolution of a video display is determined by the bandwidth of the horizontal and vertical frequencies. Therefore, the horizontal deflector for deflecting the horizontal frequency is especially important when designing a high resolution video display. In particular, the transistor used for the horizontal output should be operated within a safe operation limit, considering the condition of the gate drive, the current and voltage of the collector, switching, etc. At the same time, to enhance the resolution of the monitor, the horizontal drive circuit requires a large current and high voltage together with a short rising time and falling time.
FIG. 3 illustrates the horizontal drive circuit 42 and horizontal output circuit 43 described above. The output of the horizontal oscillation circuit (or "horizontal oscillator") 41 is amplified by a field effect transistor (FET) Q1 whose output is supplied, through the horizontal output transformer "T," to a gate of the horizontal output transistor Q2.
The horizontal drive circuit 42 includes an FET Q1, an R-C circuit, a resistor R2, and the transformer T. The gate of the FET Q1 is connected to the output of the horizontal oscillator 41. The R-C circuit includes a resistor R1 and a capacitor C1 for regulating the peak pulse of the switching signal generated by the FET Q1. The resistor R2 introduces a source voltage Vcc. The transformer T induces the source voltage Vcc, supplied through the resistor R2, according to the switching signal of the FET Q1. The peak pulse of the switching signal is regulated by the R-C circuit with the resistor R1 and the capacitor C1.
The horizontal output circuit 43 includes a horizontal output transistor Q2, capacitors C2 and C3, a damping diode D1, and a deflection yoke DY. The horizontal output transistor Q2 performs a switching operation according to the voltage level supplied from the horizontal drive circuit 42. The capacitors C2 and C3 perform a charging and discharging operation in response to the switching of the horizontal output transistor Q2. The damping diode D1 serves as a damper according to the charging and discharging of the horizontal output transistor Q2. The deflection yoke DY generates a sawtooth current according to the charging and discharging of the capacitors C2 and C3.
The horizontal drive circuit 42 requires an enhanced specification of the FET Q1 to prevent the FET Q1 from being destroyed by an over-specification voltage.